1. Field of the Invention
The present invention relates to the field of semiconductor integrated circuit manufacturing, and more specifically, to a method of creating a pattern on an EUV mask blank without particles and an EUV mask blank made with such a method.
2. Discussion of Related Art
During the fabrication of integrated circuits (IC), each semiconductor wafer is subdivided into small identical fields that are adjacent to each other. Each field includes one or more IC chips. A radiation-sensitive material, such as photoresist, is coated onto the wafer. Then a scanner with a reduction projection system is used to scan radiation across a mask and onto one field at a time to expose portions of the photoresist. The mask determines the pattern to be transferred to the wafer through the process of exposing, developing, and etching.
Deep ultraviolet (DUV) lithography uses a transmissive mask at 248 nanometers (nm), 193 nm, or 157 nm to print features with a critical dimension (CD) of 100–180 nm. Next generation lithography (NGL), such as extreme ultraviolet (EUV) lithography, can print features with smaller CD. For example, an EUV scanner may use 4 imaging mirrors and a Numerical Aperture (NA) of 0.10 to achieve a CD of 50–70 nm with a depth of focus (DOF) of about 1.00 micrometer (um). Alternatively, an EUV scanner may use 6 imaging mirrors and a NA of 0.25 to print a CD of 20–30 nm although the DOF will be reduced to about 0.17 um.
EUV lithography uses a reflective mask for exposure since nearly all condensed materials are highly absorbing in the EUV wavelength range of 11–15 nm. An EUV mask may be fabricated from an EUV mask blank after the EUV mask blank has been inspected for defects and repaired. In order to identify the location of the defects, a pattern, such as a fiducial mark, is etched into the reflective surface of an EUV mask blank. However, etching produces particles that may contaminate tools and degrade process yield.
Thus, what is needed is a method of creating a pattern on an EUV mask blank without generating particles and an EUV mask blank made with such a method.